Method and apparatus for measuring response time

Abstract

A method of measuring the response time of an electrical instrument which generates an output signal in response to the application of a specified input, wherein the output signal varies as a function of time and when subjected to a step input approaches a steady-state value, comprises the steps of: (a) applying a step input of predetermined value to the electrical instrument to generate an output signal; (b) simultaneously starting a timer; (c) comparing the output signal to a reference signal to generate a stop signal when the output signal is substantially equal to the reference signal, the reference signal being a specified percentage of the steady-state value of the output signal corresponding to the predetermined value of the step input; and (d) applying the stop signal when generated to stop the timer.

The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A method of measuring the response time of a thermocouple which generates an output signal in response to the application of a specified input, wherein the output signal varies as a function of time and when subjected to a step input approaches a steady-state value, comprises the steps of: (a) applying a step input of a predetermined value to the thermocouple to generate an output signal;   (b) simultaneously starting a timer;   (c) comparing the output signal to a reference signal to generate a stop signal when the output signal is substantially equal to the reference signal, the reference signal being a specified percentage of the steady-state value of the output signal corresponding to the predetermined value of the step input; and   (d) applying the stop signal when generated to stop the timer.   
     
     
       2. The method of claim 1 wherein the specified percentage is 63.3. 
     
     
       3. The method of claim 2 wherein the step input of a predetermined value comprises placing one junction of the thermocouple in water at 100° C. and the other end in air at room temperature. 
     
     
       4. Apparatus for measuring the response time of a thermocouple which generates an output signal in response to the application of a specified input, wherein the output signal varies as a function of time and when subjected to a step input approaches a steadystate value comprising: (a) means for applying a step input of a predetermined value to the thermocouple to generate an output signal;   (b) a timer;   (c) means for starting the timer, said timer being started simultaneously with the application of said step input;   (d) comparator means coupled to the thermocouple and to the timer to compare the output signal to a reference signal to generate a stop signal for application to the timer for stopping same when the output is substantially equal to the reference signal, the reference signal being a specified percentage of the steadystate value of the output signal corresponding to the predetermined value of the step input; and   (e) means for applying the stop signal when generated to the timer.   
     
     
       5. The apparatus of claim 4 wherein the thermocouple includes a thermocouple junction and a conductive outer shell separate from said junction, the conductive outer shell being responsive to the application of the step input to develop a start signal, and wherein said timer comprises a counter, a first gate having an output coupled to said counter, a second gate having an output coupled to said first gate, an oscillator for generating a count signal coupled to said second gate, circuit means coupling said conductive outer shell to said first gate for applying said start signal thereto, said comparator being coupled to said second gate for applying said stop signal thereto, said first gate being responsive to said start signal to couple said count signal to said counter, and said second gate being responsive to said stop signal to block said count signal from said counter. 
     
     
       6. The apparatus of claim 5 wherein the specified percentage is 63.3. 
     
     
       7. The apparatus of claim 5 wherein the means for applying a step input of a predetermined value comprises placing one end of the thermocouple and the conductive outer shell in water at 100° C. and the other end in air at room temperature.